This invention relates generally to dynamo-electric machines and, more particularly, to structures for reducing vibration within the dynamo-electric machine.
Dynamo-electric machine rotors formed of a stack of laminations having slots equally spaced from one another about the periphery of each lamination are known. Such rotors are often used in inductive AC motors and generators and include conducting members that extend axially along the rotor through aligned slots of the stacked laminations. The conducting members or bars interact with a rotating magnetic field created in an air gap between the outer circumference of the rotor and the inner circumference of the machine stator. Windings embedded in slots between radially inwardly projecting teeth of the stator, adjacent the air gap, are connected to the AC mains, and the stator winding conductors pass through a certain order of the stator slots so as to cause magnetic flux in the air gap to rotate in synchronism with the frequency of the AC mains.
The rotor bars may be cast in situ in the rotor slots, or may be pressed into the rotor slots. Ends of the bars are coupled by electrically conductive end-rings which may be integrally formed with the bars or may be brazed to the ends of the bars.
During operation, maintaining continuous contact between the rotor bars and the rotor core facilitates reducing rotor vibration. More specifically, continuous contact with the rotor bars facilitates controlling high frequency vibration caused by loose bars. Additionally, accommodating thermal expansion of the rotor components reduces rotor imbalance caused by reaction forces generated by the differential expansion of the rotor bars and slots. Such reaction forces are proportional to slot frictional forces, which oppose rotor bar expansion and may cause rotor unbalance problems. In operation, the temperature of the motor will increase with load. In some motors, the magnitude and angle of the vibration changes noticeably with rotor temperature because of non-uniform expansion of the rotor. Such non-uniform expansion may result from some rotor bars locking in their slots when the slot frictional force exceeds the thermal elongation differential between bar and slot.